The present invention relates generally to diagnostic imaging and, more particularly, to an x-ray tube assembly having multiple x-ray sources. The present invention further relates to an anode assembly having multiple electron targets such that multiple x-ray fan beams may be produced.
X-ray or radiographic imaging is the basis of a number of diagnostic imaging systems. Computed tomography (CT) is one example of such a system that is predicated upon the acquisition of data using the principles of radiography. Typically, in CT imaging systems, a single x-ray source emits a single fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
CT systems, as well as x-ray systems, typically utilize a rotating anode during the data acquisition process. Rotating the anode helps fan the x-ray fan beam, but, more importantly, reduces the thermal load on the anode. That is, the anode typically includes a single target electrode that is mounted or integrated with an anode disc. The anode disc is rotated by an induction motor during data acquisition. Since the electrons striking the anode deposit most of their energy as heat, with a small fraction emitted as x-rays, producing x-rays in quantities sufficient for acceptable image quality generates a large amount of heat. A number of techniques have been developed to accommodate the thermal load placed on the anode during the x-ray generate process.
For example, advancements in the detection of x-ray attenuation has allowed for a reduction in x-ray dose necessary for image acquisition. X-ray dose and tube current are directly related and, as such, a reduction in tube current results in a reduction in x-ray dosage. A drop in tube current, i.e. reduction in the number of striking electrons on the anode target, reduces the thermal load placed on the anode target during data acquisition. Simply, less power is needed to generate the x-rays necessary for data acquisition. X-rays are generated as a result of electrons emitted from a cathode striking a target electrode mounted to or integrated with the anode disc. The number of electrons emitted depends in part of the voltage potential placed across the cathode and anode. Increasing the voltage potential increases the number of emitted electrons. Since a minimum number of electrons must be generated for meaningful data acquisition, a mere reduction in tube current is insufficient to address the thermal load on the anode resulting from x-ray generation.
Another approach is predicated upon the spreading of the generated heat across the surface and mass of the anode disc. By rotating the anode disc as electrons are striking the target electrode, the heat generated therefrom may be spread across the anode disc rather than across the target electrode alone. This rotation of the anode disc effectively reduces the thermal load placed on the target electrode. As a result, tube current may be increased without thermal overloading of the anode. Generally, the faster the anode disc is rotated the higher the tube current that may be used.
Increasing the tube current and effectively the power levels of the x-ray tube assembly is particularly desirable for short duration high power reconstruction protocols. With these protocols, the gantry is caused to rotate at significantly fast rotational speeds. Through increased rotational gantry speed, the overall exam time may be decreased. Decreasing the overall exam or scan time improves patient throughput and reduces patient discomfort which reduces patient-induced motion artifacts in the reconstructed image. To support faster gantry speeds, the x-ray tube must output sufficiently more instantaneous power which is required for short duration protocols.
To provide the requisite instantaneous power needed for short duration protocols, the x-ray tube must output more power without exceeding the thermal load of the target electrode. As mentioned above, rotating the anode disc during x-ray generation reduces the thermal load on the electrode target. Known CT systems utilize a rotating anode disc and due to material strength limitations, it is not feasible to simply increase the rotational speed of the anode disc or its size. Another means to increase the power output of the x-ray tube is to simply increase its size. Increasing the tube size and mass however is also not a feasible solution. The gantry must support rotation of the x-ray tube and any increase in x-ray tube size and weight increases the support burden placed on the gantry. As a result, the size of the gantry would have to be increased yielding a much larger CT scanner.
It would therefore be design a method and system for increasing the power output of an x-ray tube assembly without increasing its size or mass.